IgE plays a central role in mediating type I hypersensitivity reactions that are responsible for causing allergic diseases, including allergic asthma, allergic rhinitis, atopic dermatitis, and others. Allergic reactions are the responses of the immune system toward harmless environmental substances, such as dust mites, tree and grass pollens, certain food and drugs, and bee and fire ant bites. In such reactions, the binding of an allergen to IgE on the surface of basophils and mast cells causes the cross-linking of IgE and the aggregation of the underlying receptors of IgE.Fc, the type I IgE.Fc receptors, or FcεRI. This receptor aggregation subsequently activates the signaling pathway leading to the exocytosis of granules and the release of pharmacologic mediators, such as histamine, leukotrienes, tryptase, cytokines and chemokines. The release of those mediators from mast cells and basophils causes the various pathological manifestations of allergy.
Anti-IgE antibodies that bind to free IgE in the blood and in interstitial fluid and to mIgE on B cells, but not to IgE bound by FcεRI on basophils and mast cells, have been developed for treating IgE-mediated allergic diseases. The treatment with a humanized anti-IgE antibody, omalizumab (trade name Xolair), has shown multiple pharmacologic effects in attenuating type I hypersensitivity in various allergic indications. The antibody binds to IgE with high affinity at a site in the CH3 domain of Fc that overlaps with the binding site of FcεRI. Hence, the therapy is based on the binding of the antibody to free IgE and to mIgE on B lymphoblasts and on memory B cells, which leads to the reduction of overall free IgE level in blood and interstitial fluid.
The binding of anti-IgE to free IgE further prevents IgE binding to FcεRI on the surface of basophils and mast cells. As the FcεRI unoccupied by IgE is unstable and subsequently internalized and degraded, the depletion of free IgE with anti-IgE binding also gradually down-regulates FcεRI on basophils and mast cells. Evidence for other effects of the antibody therapy has been found, including the neutralization of cytokinergic activities, the attenuation of overall inflammatory activity, and possibly the sweeping of allergens through the accumulation of IgE-anti-IgE immune complexes.
One of the inventors (T. W. Chang) of this invention discovered that in addition to the antigenic site on CH3 of IgE that omalizumab binds to, another antigenic site, referred to as CεmX, exists on human mIgE for the targeting of mIgE-expressing B lymphocytes. CεmX is a 52-amino acid segment located between the CH4 domain and the C-terminal membrane-anchoring segment of human membrane-bound ε chain (mε). It has been shown that in most human subjects studied, the mε without CεmX (mεS) accounts for minute proportions, whereas mε chain with CεmX (mεL) is dominantly expressed. The mRNAs for ε chain of free, secreted IgE and for mεS and mεL of mIgE are all derived from alternative splicing of the ε RNA transcript. The amino acid and nucleotide sequences of CεmX are unique in the entire protein and DNA databases. Therefore, CεmX provides a unique antigenic site for targeting mIgE and the mIgE-expressing B cells.
The research group of Chang previously reported the development of several CεmX-specific mouse monoclonal antibodies, including a20, which can bind to recombinant proteins containing CεmX segment and to cells of SKO-007 cell line, which was a human myeloma-derived cell line expressing human mIgE, and to cells of a CHO cell line, which was transfected with the gene corresponding to the segment from CH2 domain through the cytoplasmic end of mεL (mεL(CH2-CM); CM: cytoplasm). The monoclonal antibody a20 and all antibodies developed earlier were found to bind to an 8-a. a. peptidic region, RADWPGPP (SEQ ID NO:1), residues #45-52, at the C-terminal end of the 52 aa CεmX domain.